The increase in the amount of data handled by, for example, computer systems has lead to demands for data storage back up devices that use magnetic tape. Magnetic tape media remains an economical medium for storing large amounts of data. For example, magnetic tape cartridges, or large spools of magnetic tape are often used to back up large amounts of data for large computing centers. Magnetic tape cartridges also find application in the backup of data stored on smaller computers such as workstations, desktop or laptop computers. Increasing linear recording density or track density (TPI: Track Per Inch) is the key to improving memory capacity of magnetic recording tape systems which use linear magnetic tape with multiple recording tracks in the lengthwise direction.
One type of data storage system is a linear tape drive. Many linear tape drive systems use a track method for writing data to the tape and reading data from the magnetic tape. Specifically, multiple servo bands extend along the lengthwise direction of the magnetic tape across the width of the tape. Multiple data bands are formed between the servo bands. The data bands in the lengthwise direction of the magnetic tape have many parallel data tracks.
Magnetic tape is used to record and replay multiple data tracks simultaneously from the selected data band using a multi-channel magnetic head. The magnetic head includes two rows of recording and playback magnetic head elements which are combinations of multiple recording magnetic head elements and playback magnetic head elements arranged across the width of a track. The distance between the recording and reproducing magnetic head elements in each row matches the spacing of the data tracks between data bands. Both ends of the rows of recording and playback magnetic head elements have a playback magnetic head element that reads servo signals from the servo band on both sides of a data band during recording and playback. The servo signals are used to locate the recording and playback magnetic head element.
Generally, the magnetic tape moves in round trips across the magnetic head. Different data tracks can be written or read by moving the magnetic head a predetermined amount across the width of the tape. During recording, whichever way the tape is moving, the corresponding track is recorded by a recording magnetic head element which is in a row on the leading side of the magnetic tape each time the magnetic tape is transferred. This recording condition is monitored by playback magnetic head elements in a row on the trailing side. During playback, recorded data signals are reproduced by any playback magnetic head elements in two rows.
During recording and playback, servo signals are read from the track by playback magnetic head elements on both ends of the row of magnetic head elements. Servo bands are located on both sides of the data band where recording and playback is done. These servo bands control the location of the magnetic head which transfers data from the magnetic head to the data track.
For example, linear tape open (LTO) drives are representative of linear tape product and are designed to respond to demand for higher track density while also providing a high range tracking servo for following at an increased speed. LTO drives have a rough positioning system which selects the proper track, and a fine positioning system which uses a servo for position control. Rough positioning is required so that the servo can cover a wider area at high speed because of the higher track density of high density linear tape.
The fine tracking actuator for a linear tape drive is typically a voice coil motor (VCM). However, the resonant frequency of the VCM is usually a lower frequency, such as 200 Hz, and has a narrow servo range. In general, the servo range of the actuator is limited by the resonant frequency of the actuator itself. Consequently, increasing the resonant frequency of the actuator is required for increasing the range.
When the resonant frequency is close to the normal range, disturbances, such as noise excite the head at this resonant frequency. Therefore, it is often necessary to lower the Q value that indicates the sharpness of the resonant peak. However, this has failed to attain a sufficient servo range. As an alternate method, the use of a fine positioning structure that uses a bimodal construction made of laminated piezoelectric elements has been suggested. This fine positioning system has a higher resonant frequency compared to the VCM and can widen the servo range. However, the success of the fine positioning structure has further increased the demand for an even higher servo range.